Unbridled, unscrupulous, and without fear of consequences
Often used when describing the efforts of bad people
Negative
由于执法方面的包庇，造假者更加肆无忌惮 | Yóuyú zhífǎ fāngmiàn de bāobì, zàojiǎ zhě gèngjiā sìwújìdàn
Under the protection of law enforcement officials, the counterfeiters grow even more brazen
[Source]
歹徒肆无忌惮地冲进了金银店铺 | Dǎitú sìwújìdàn de chōng jìnle jīn yín diànpù
The criminal unscrupulously charged into the bank
[Source]
None
None
This is an HSK chengyu
《礼记》(Lǐ Jì, "The Book of Rites"), one of the five classic works of Confucianism
This chengyu is from a line in the work listed in the "Origin" section above